A system is known where visible light on which data are superposed is transmitted from a transmitter to a receiver. The transmitter blinks a light source such as a light emitting diode (LED) which emits a visible light according to the data to be transmitted. The receiver receives the data by photographing and demodulating the visible light emitted from the light source by using a photo diode (PD) or an image sensor. Particularly, in a receiver using the image sensor, since the light source needs to be recognized on the sensor during the reception period, it is preferable to implement the previewing over the entire angle of viewing at the same time of the reception in order to improve usability.
In the transmission system, by setting the frequency of the light source of the transmitter to be high so that the blinking of the light source is not perceived, information can be transmitted without disturbing normal illumination or general operations of a display. On the other hand, since a low power and low cost receiver is desired, it is preferable that the frame rate of the receiver is low. In general, it is difficult for a receiver having a low frame rate to perceive blinking of the light source at a high frequency.
In order to improve an effective frame rate, a manner of accessing only a portion of the area which can be photographed by the receiver can be considered. However, since a peripheral portion of the light source is not accessed, there is a problem in that previewing over the entire angle of viewing cannot be performed. In this case, it is difficult to find the position of the light source or to handle a plurality of the light sources. On the other hand, if an image sensor having a specialized structure is used in order to perform previewing, there is a problem of an increase in costs of implementation.